Independent Submission F. Templin
Request for Comments: 5720 Boeing Phantom Works
Category: Informational February 2010
ISSN: 2070-1721
Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)
Abstract
RANGER is an architectural framework for scalable routing and
addressing in networks with global enterprise recursion. The term
"enterprise network" within this context extends to a wide variety of
use cases and deployment scenarios, where an "enterprise" can be as
small as a Small Office, Home Office (SOHO) network, as dynamic as a
Mobile Ad Hoc Network, as complex as a multi-organizational
corporation, or as large as the global Internet itself. Such
networks will require an architected solution for the coordination of
routing and addressing plans with accommodations for scalability,
provider-independence, mobility, multihoming, and security. These
considerations are particularly true for existing deployments, but
the same principles apply even for clean-slate approaches. The
RANGER architecture addresses these requirements and provides a
comprehensive framework for IPv6/IPv4 coexistence.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5720.
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................4
3. The RANGER Architecture .........................................7
3.1. Routing and Addressing .....................................7
3.2. The Enterprise-within-Enterprise Framework .................9
3.3. Virtual Enterprise Traversal (VET) ........................12
3.3.1. RANGER Organizational Principles ...................12
3.3.2. RANGER End-to-End Addressing Example ...............14
3.3.3. Dynamic Routing and On-Demand Mapping ..............14
3.3.4. Support for Legacy RLOC-Based Services .............16
3.4. Subnetwork Encapsulation and Adaptation Layer (SEAL) ......18
3.5. Mobility Management .......................................18
3.6. Multihoming ...............................................20
3.7. Implications for the Internet .............................20
4. Related Initiatives ............................................21
5. Security Considerations ........................................22
6. Acknowledgements ...............................................23
7. References .....................................................23
7.1. Normative References ......................................23
7.2. Informative References ....................................24
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1. Introduction
RANGER is an architectural framework for scalable routing and
addressing in networks with global enterprise recursion. The term
"enterprise network" within this context extends to a wide variety of
use cases and deployment scenarios, where an "enterprise" can be as
small as a SOHO network, as dynamic as a Mobile Ad Hoc Network, as
complex as a multi-organizational corporation, or as large as the
global Internet itself. Such networks will require an architected
solution for the coordination of routing and addressing plans with
accommodations for scalability, provider-independence, mobility,
multihoming, and security. These considerations are particularly
true for existing deployments, but the same principles apply even for
clean-slate approaches. The RANGER architecture addresses these
requirements and also provides a comprehensive framework for IPv6/
IPv4 coexistence [COEXIST].
RANGER provides a unifying architecture for enterprises that contain
one or more distinct interior IP routing and addressing domains (or
"Routing LOCator (RLOC) space"), with each distinct RLOC space
containing one or more organizational groupings. Each RLOC space may
coordinate their own internal addressing plans independently of one
another, such that limited-scope addresses (e.g., [RFC1918] private-
use IPv4 addresses) may be reused with impunity to provide unlimited
scaling through spatial reuse. Each RLOC space therefore appears as
an enterprise unto itself, where organizational partitioning of the
enterprise into one or more "sub-enterprises" (or "sites") is also
possible and beneficial in many scenarios. Without an architected
approach, routing and addressing within such a framework would be
fragmented due to address/prefix reuse between disjoint enterprises.
With RANGER, however, multiple enterprises can be linked together to
provide a multi-hop transit for nodes attached to enterprise edge
networks that use Endpoint Interface iDentifier (EID) addresses taken
from an IP addressing range that is distinct from any RLOC space.
RANGER is recursive in that multiple enterprises can be joined
together in a nested "enterprise-within-enterprise" fashion, where
each enterprise also connects edge networks with nodes that configure
addresses taken from EID space to support edge/core separation. In
this way, the same RANGER principles that apply in lower levels of
recursion can extend upwards to parent enterprises and ultimately to
the core of the global Internet itself. Furthermore, it is also
worth considering whether today's global Internet represents a
limiting condition for recursion -- in particular, whether other
internets could be manifested as "parallel universes" and joined
together at still higher levels of recursion.
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The RANGER architecture is manifested through composite technologies,
including Virtual Enterprise Traversal (VET) [VET], the Subnetwork
Encapsulation and Adaptation Layer (SEAL) [SEAL], and the Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214]. Other
mechanisms such as IPsec [RFC4301] are also in scope for use within
certain scenarios.
Noting that combinations with still other technologies are also
possible, the issues addressed either in full or in part by RANGER
include:
o scalable routing and addressing
o provider-independent addressing and its relation to provider-
aggregated addressing
o site mobility and multihoming
o address and prefix autoconfiguration
o border router discovery
o router/host-to-router/host tunneling
o neighbor discovery over tunnels
o MTU determination for tunnels
o IPv6/IPv4 coexistence and transition
Note that while this document primarily uses the illustrative example
of IPv6 [RFC2460] as a virtual overlay over IPv4 [RFC0791] networks,
it is important to note that the same architectural principles apply
to any combination of IPvX virtual overlays over IPvY networks.
2. Terminology
Routing Locator (RLOC)
an IPv4 or IPv6 address assigned to an interface in an enterprise-
interior routing region. Note that private-use IP addresses are
local to each enterprise; hence, the same private-use addresses
may appear within disjoint enterprises.
Endpoint Interface iDentifier (EID)
an IPv4 or IPv6 address assigned to an edge network interface of
an end system. Note that EID space must be separate and distinct
from any RLOC space.
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commons
an enterprise-interior routing region that provides a subnetwork
for cooperative peering between the border routers of diverse
organizations that may have competing interests. A prime example
of a commons is the Default-Free Zone (DFZ) of the global
Internet. The enterprise-interior routing region within the
commons uses an addressing plan taken from RLOC space.
enterprise
the same as defined in [RFC4852], where the enterprise deploys a
unified RLOC space addressing plan within the commons but may also
contain partitions with disjoint RLOC spaces and/or organizational
groupings that can be considered as enterprises unto themselves.
An enterprise therefore need not be "one big happy family", but
instead provides a commons for the cooperative interconnection of
diverse organizations that may have competing interests (e.g.,
such as the case within the global Internet DFZ).
Enterprise networks are typically associated with large
corporations or academic campuses; however, the RANGER
architectural principles apply to any network that has some degree
of cooperative active management. This definition therefore
extends to home networks, small office networks, ISP networks, a
wide variety of Mobile Ad Hoc Networks (MANETs), and even to the
global Internet itself.
site
a logical and/or physical grouping of interfaces within an
enterprise commons, where the topology of the site is a proper
subset of the topology of the enterprise. A site may contain many
interior sites, which may themselves contain many interior sites
in a recursive fashion.
Throughout the remainder of this document, the term "enterprise"
refers to either enterprise or site, i.e., the RANGER principles
apply equally to enterprises and sites of any size or shape. At
the lowest level of recursive decomposition, a singleton
Enterprise Border Router can be considered as an enterprise unto
itself.
Enterprise Border Router (EBR)
a router at the edge of an enterprise that is also configured as a
tunnel endpoint in an overlay network. EBRs connect their
directly attached networks to the overlay network, and connect to
other networks via IP-in-IP tunneling across the commons to other
EBRs. This definition is intended as an architectural equivalent
of the functional term "EBR" defined in [VET].
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Enterprise Border Gateway (EBG)
an EBR that also connects the enterprise to provider networks
and/or to the global Internet. EBGs are typically configured as
default routers in the overlay and provide forwarding services for
accessing IP networks not reachable via an EBR within the commons.
This definition is intended as an architectural equivalent of the
functional term "EBG" defined in [VET], and is synonymous with the
term "default mapper" used in other contexts (e.g., [JEN]).
Ingress Tunnel Endpoint (ITE)
a host or router interface that encapsulates inner IP packets
within an outer IP header for transmission over an enterprise-
interior routing region to the RLOC address of an Egress Tunnel
Endpoint (ETE).
Egress Tunnel Endpoint (ETE)
a host or router interface that receives encapsulated packets sent
to its RLOC address, decapsulates the inner IP packets, then
delivers them to the EID address of the final destination.
overlay network
a virtual network manifested by routing and addressing over
virtual links formed through automatic tunneling. An overlay
network may span many underlying enterprises.
Provider-Independent (PI) prefix
an IPv6 or IPv4 EID prefix (e.g., 2001:DB8::/48, 192.0.2/24, etc.)
that is routable within a limited scope and may also appear in
enterprise mapping tables. PI prefixes that can appear in mapping
tables are typically delegated to a Border Router (BR) by a
registry but are not aggregated by a provider network. Local-use
IPv6 and IPv4 prefixes (e.g., FD00::/8, 192.168/16, etc.) are
another example of a PI prefix, but these typically do not appear
in mapping tables.
Provider-Aggregated (PA) prefix
an IPv6 or IPv4 EID prefix that is either derived from a PI prefix
or delegated directly to a provider network by a registry.
Although not widely discussed, it bears specific mention that a
prefix taken from a delegating router's PI space becomes a PA
prefix from the perspective of the requesting router.
Additionally, RANGER provides an informative consideration of
functional specifications and operational practices outlined in other
documents. These documents include:
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6over4
Transmission of IPv6 over IPv4 Domains without Explicit Tunnels
[RFC2529]; functional specifications and operational practices for
automatic tunneling of unicast/multicast IPv6 packets over
multicast-capable IPv4 enterprises.
ISATAP
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
[RFC5214]; functional specifications and operational practices for
automatic tunneling of unicast IPv6 packets over unicast-only IPv4
enterprises.
VET
Virtual Enterprise Traversal (VET) [VET]; functional
specifications and operational practices for automatic tunneling
of both unicast and multicast IP packets with provisions for
address/prefix autoconfiguration, provider-independent addressing,
mobility, multihoming, and security. VET is descended from both
6over4 and ISATAP and is also known as "ISATAP version 2
(ISATAPv2)".
SEAL
Subnetwork Encapsulation and Adaptation Layer (SEAL) [SEAL]; an
encapsulation sublayer that provides an extended IP Identification
field and mechanisms for link MTU adaptation over tunnels.
3. The RANGER Architecture
The RANGER architecture enables scalable routing and addressing in
networks with global enterprise recursion while sustaining support
for legacy networks and services. Key to this approach is a
framework that accommodates interconnection of diverse organizations
across a commons that have a mutual spirit of cooperation but also
have the potential for competing interests. The following sections
outline the RANGER architecture within the context of anticipated use
cases:
3.1. Routing and Addressing
The Internet today is facing "growing pains", with indications that
core Routing Information Base (RIB) scaling may not be sustainable
over the long term and that the remaining space for IPv4 address
allocations may be depleted in the near future. Therefore, there is
an emerging need for scalable routing and addressing solutions. It
must further be noted that the same solutions selected to address
global Internet routing and addressing scaling can apply equally for
large enterprises -- or for any enterprise that would benefit from a
separation of core and edge addressing domains.
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RANGER supports scalable routing through an approach that parallels
the "New Scheme for Internet Routing and Addressing" described in
[RFC1955]. This approach is also commonly known as "map-and-encaps".
In this approach, an Ingress Tunnel Endpoint (ITE) that must forward
an IP packet first consults a mapping system to discover a mapping
for the destination Endpoint Interface iDentifier (EID) to a Routing
LOCator (RLOC) assigned to an Egress Tunnel Endpoint (ETE). The
mapping system is typically maintained as a per-enterprise
distributed database that is synchronized among a limited set of
mapping agents. Distributed database management alternatives include
a routing protocol instance maintained by Enterprise Border Gateways
(EBGs), a DNS reverse zone distributed among a restricted set of
caching servers, etc. Mapping entries are inserted into the mapping
system through administrative configuration, automated prefix
registrations, etc.
RANGER allows for an ITE to either consult the mapping system itself
(while delaying or dropping initial IP packets) or forward initial
packets to an EBG acting as a "default mapper". In either case, the
ITE receives a mapping reply that it can use to populate its
Forwarding Information Base (FIB). The choice of mapping approaches
must be considered with respect to the individual enterprise network
scenario, e.g., forwarding to an EBG may be more appropriate in some
scenarios while ITE self-discovery may be more appropriate in others.
Use of other mapping mechanisms is also possible according to the
specific enterprise scenario.
After discovering the mapping, the ITE encapsulates inner IP packets
in an outer IP header for transmission across the commons to the RLOC
address of an ETE. The ETE in turn decapsulates the packets and
forwards them over the next hop toward the EID address of the final
destination. Therefore, the Routing Information Base (RIB) within
the commons only needs to maintain state regarding RLOCs and not
EIDs, while the synchronized EID-to-RLOC mapping state is maintained
by a smaller number of nodes and is not subject to oscillations due
to link state changes within the commons. Finally, EIDs are routable
only within a limited scope within edge networks (which may be as
small as node-local scope in the limiting case).
RANGER supports scalable addressing by selecting a suitably large EID
addressing range that is distinct and kept separate from any
enterprise-interior RLOC addressing ranges. It should therefore come
as no surprise that taking EID space from the IPv6 addressing
architecture should lead to a viable, scalable addressing
alternative, while taking EID space from the (already exhausted) IPv4
addressing architecture may not.
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3.2. The Enterprise-within-Enterprise Framework
Enterprise networks traditionally distribute routing information via
Interior Gateway Protocols (IGPs) such as Open Shortest Path First
(OSPF), while large enterprises may even use an Exterior Gateway
Protocol (EGP) internally in place of an IGP. Thus, it is becoming
increasingly commonplace for large enterprises to use the Border
Gateway Protocol (BGP) internally and independently from the BGP
instance that maintains the RIB within the global Internet DFZ.
As such, large enterprises may run an internal instance of BGP across
many internal Autonomous Systems (ASs). Such a large enterprise can
therefore appear as an internet unto itself, albeit with default
routes leading to the true global Internet. Additionally, each
internal AS within such an enterprise may itself run BGP internally
in place of an IGP, and can therefore also appear as an independent,
lower-tier enterprise unto itself. This enterprise-within-enterprise
framework can be extended in a recursive fashion as broadly and as
deeply as desired to achieve scaling factors as well as
organizational and/or functional compartmentalization, e.g., as shown
in Figure 1.
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,---------------.
,-' Global `-.
Figure 1: Enterprise-within-Enterprise Framework
Figure 1 depicts an enterprise 'E1' connected to the global IPv6/IPv4
Internet via routers 'R1' through 'Rn' and additional enterprises
'E2' through 'EN' that also connect to the global Internet. Within
the 'E1' commons, there may be arbitrarily many hosts, routers, and
networks (not shown in the diagram) that use addresses taken from
RLOC space and over which both encapsulated and unencapsulated IP
packets can be forwarded. There may also be many lower-tier
enterprises, 'E1.1' through 'E1.m' (shown in the diagram), that
interconnect within the 'E1' commons via Enterprise Border Routers
(EBRs), depicted as 'X1' through 'X9' (where 'X1' through 'X9' see
'R1' through 'Rn' as EBGs). Within each 'E1.*' enterprise, there may
also be arbitrarily many lower-tier enterprises that interconnect
within the 'E1.*' commons via EBRs, depicted as 'Y1' through 'Y9' in
the diagram (where 'Y1' through 'Y9' see 'X1' through 'X9' as EBGs).
This recursive decomposition can be nested as deeply as desired and
ultimately terminates at singleton nodes such as those depicted as
'V', 'W', and 'Z' in the diagram.
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It is important to note that nodes such as 'V', 'W', and 'Z' may be
simple hosts or they may be EBRs that attach arbitrarily complex edge
networks with addresses taken from EID space. Such edge networks
could be as simple as a home network behind a residential gateway or
as complex as a major corporate/academic campus, a large service
provider network, etc.
Again, this enterprise-within-enterprise framework can be recursively
nested as broadly and deeply as desired. From the highest level of
the recursion, consider now that the global Internet itself can be
viewed as an "enterprise" that interconnects lower-tier enterprises
E1 through EN such that all RANGER architectural principles apply
equally within that context. Furthermore, the RANGER architecture
recognizes that the global Internet need not represent a limiting
condition for recursion, but rather allows that other internets could
be manifested as "parallel universes" and joined together at still
higher levels of recursion.
As a specific case in point, the future global Aeronautical
Telecommunications Network (ATN), under consideration within the
civil aviation industry [BAUER], will take the form of a large
enterprise network that appears as an internet unto itself, i.e.,
exactly as depicted for 'E1' in Figure 1. Within the ATN, there will
be many Air Communications Service Provider (ACSP) and Air Navigation
Service Provider (ANSP) networks organized as autonomous systems
internal to the ATN, i.e., exactly as depicted for 'E1.*' in the
diagram. The ACSP/ANSP network EBGs will participate in a BGP
instance internal to the ATN, and may themselves run independent BGP
instances internally that are further sub-divided into lower-tier
enterprises organized as regional, organizational, functional, etc.
compartments. It is important to note that, while ACSPs/ANSPs within
the ATN will share a common objective of safety-of-flight for civil
aviation services, there may be competing business/social/political
interests between them, such that the ATN is not necessarily "one big
happy family". Therefore, the model parallels that of the global
Internet itself.
Such an operational framework may indeed be the case for many next-
generation enterprises. In particular, although the routing and
addressing arrangements of all enterprises will require a mutual
level of cooperative active management at a certain level, free
market forces, business objectives, political alliances, etc. may
drive internal competition.
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3.3. Virtual Enterprise Traversal (VET)
Within the enterprise-within-enterprise framework outlined in Section
3.2, the RANGER architecture is based on overlay networks manifested
through Virtual Enterprise Traversal (VET) ([VET], [RFC5214]). The
VET approach uses automatic IP-in-IP tunneling in which ITEs
encapsulate EID-based inner IP packets within RLOC-based, outer IP
headers for transmission across the commons to ETEs.
For each enterprise they connect to, EBRs that use VET configure a
Non-Broadcast, Multiple Access (NBMA) interface known as a "VET
interface" that sees all other EBRs within the enterprise as
potential single-hop neighbors from the perspective of the inner IP
protocol. This means that, for many enterprise scenarios, standard
neighbor discovery mechanisms (e.g., router advertisements,
redirects, etc.) can be used between EBR pairs. This gives rise to a
data-driven model in which neighbor relationships are formed based on
traffic demand in the data plane, which in many cases can relax the
requirement for dynamic routing exchanges across the overlay in the
control plane.
When multiple VET interfaces are linked together, end-to-end
traversal is seen as multiple VET hops from the perspective of the
inner IP protocol. In that case, transition between VET interfaces
entails a "re-encapsulation" approach in which a packet that exits
VET interface 'i' is decapsulated then re-encapsulated before it is
forwarded into VET interface 'i+1'. For example, if an end-to-end
path between two EID-based peers crosses N distinct VET interfaces, a
traceroute would show N inner IP forwarding hops corresponding to the
portions of the path that traverse the VET interfaces.
VET and its related works specify necessary mechanisms and
operational practices to manifest the RANGER architecture. The use
of VET in conjunction with SEAL (see Section 3.4) is essential in
certain deployments to avoid issues related to source address
spoofing and black holing due to path Maximum Transmission Unit (MTU)
limitations. (The use of VET in conjunction with IPsec [RFC4301] may
also be necessary in some enterprise network scenarios.) The
following sections discuss operational considerations and use cases
within the VET approach.
3.3.1. RANGER Organizational Principles
Figure 2 below depicts a vertical slice (albeit represented
horizontally) from the enterprise-within-enterprise framework shown
in Figure 1:
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RFC 5720 RANGER February 2010
+------+
| IPv6 |
" " " " " " " "" " " " " " " " " " " " " " " " |Server|
" " +--+---+
" . . . . . . . . . . . . . . . " |
" . . . . . . " |
" . +----+ v +--- + v +----+ v +----+ +-----+-------+
" . | V += e =+ Y1 += e =+ X2 += e =+ R2 +==+ Internet |
" . +-+--+ t +----+ t +----+ t +----+ +-----+-------+
" . | 1 . . 2 . . 3 . " |
" . H . . . . . " |
" . . . . . . . . . . . . . . " +--+---+
" " | IPv4 |
" 10/8 10/8 10/8 " |Server|
" " " " " " " " " " " " " " "" " " " " " " " | S2 |
+------+
Figure 2: Virtual Enterprise Traversal
Within this vertical slice, each enterprise within the 'E1' recursive
hierarchy is spanned by VET interfaces, represented as 'vet1' through
'vet3'. Each VET interface within this framework is a Non-Broadcast,
Multiple Access (NBMA) interface that connects all EBRs within the
same enterprise. Each enterprise within the 'E1' hierarchy may
comprise a smaller topological region within a larger RLOC space, or
they may configure an independent RLOC space from a common (but
spatially reused) limited-scope prefix, e.g., depicted as multiple
disjoint instances of '10/8' in the diagram.
In the RANGER approach, EBRs within lower-tier enterprises coordinate
their EID prefixes with EBGs that connect to an upper-tier
enterprise. EID prefixes could be either provider-independent (PI)
prefixes owned by the EBR or provider-aggregated (PA) prefixes
delegated by the EBG. In either case, EID prefixes must be
coordinated with the enterprise routing/mapping systems.
When PA EID prefixes are used, the EBR for each 'E1*' enterprise
receives an EID prefix delegation from a delegating EBG in a parent
enterprise. In this example, when 'R2' is a delegating router for
the prefix '2001:DB8::/40', it may delegate '2001:DB8::/48' to 'X2',
which in turn delegates '2001:DB8::/52' to 'Y1', which in turn
delegates '2001:DB8::/56' to 'V'. The preferred mechanism for this
recursive PA prefix sub-delegation is DHCP Prefix Delegation
[RFC3633], which also arranges for publication of the prefixes in the
enterprise routing system.
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When PI EID prefixes are used, individual EBRs (e.g., 'V') register
their PI prefixes (e.g., '2001:DB1:10::/56') by sending Router
Advertisement (RA) messages to EBGs within the enterprise to assert
prefix ownership. When stronger authentication is necessary, the
EBRs can digitally sign the messages using the mechanisms specified
for SEcure Neighbor Discovery (SEND) [RFC3971]. EBGs that receive
the RAs (e.g., 'Y1') first verify the sender's credentials, then
register the prefixes in the enterprise mapping system. Next, they
forward a proxied version of the RA to EBGs within their parent
enterprises (e.g., 'X2'). This proxying process continues up the
recursive hierarchy until a default-free commons is reached. (In
this case, the proxying process ends at 'R2'). After the initial
registration, the EBR that owns the PI prefixes must periodically
send additional RAs to update prefix expiration timers.
3.3.2. RANGER End-to-End Addressing Example
In Figure 2, an IPv6 host 'H' that is deeply nested within Enterprise
'E1' connects to IPv6 server 'S1', located somewhere on the IPv6
Internet. 'H' is attached to a shared link with IPv6/IPv4 dual-stack
router 'V', which advertises the IPv6 prefixes '2001:DB8:0:0::/64'
and '2001:DB8:10:0::/64'. 'H' uses standard IPv6 neighbor discovery
mechanisms to discover 'V' as a default IPv6 router that can forward
its packets off the local link, and configures addresses from both of
the advertised prefixes. 'V' in turn sees node 'Y1' as an EBG that
is reachable via VET interface 'vet1' and that can forward packets
toward IPv6 server 'S1'. Similarly, node 'Y1' is an EBR on the
enterprise spanned by 'vet2' that sees 'X2' as an EBG, and node 'X2'
is an EBR on 'vet3' that sees 'R2' as an EBG. Ultimately, 'R2' is an
EBR that connects 'E1' to the global Internet.
3.3.3. Dynamic Routing and On-Demand Mapping
In the example shown in Figure 2, 'V', 'Y1', 'X2', and 'R2' configure
separate VET interfaces for each enterprise they connect to in order
to discover routes through a dynamic routing protocol and/or mapping
database lookups. After tunnels 'vet1' through 'vet3' are
established, the EBRs connected to a VET interface can run a dynamic
routing protocol such as OSPVFv3 [RFC5340] and exchange topology
information over the VET interface using the NBMA interface model.
In this way, each EBR can discover other EBRs on the link via routing
protocol control message exchanges.
In a second example, Figure 3 depicts an instance of on-demand
discovery of more specific routes in which an IPv6 end system 'H'
connects to a peer end system 'J', located in a different
organizational entity within 'E1':
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+------+
| IPv6 |
" " " " " " " "" " " " " " " " " " " " " " " " |Server|
" " +--+---+
" . . . . . . . . . . . . . . . " |
" . . . . . . " |
" . +----+ v +----+ v +----+ +----+ +-----+-------+
" . | V += e =+ Y1 += e =+ X2 += =+ R2 +==+ Internet |
" . +-+--+ t +----+ t +----+ +----+ +-----+-------+
" . | 1 . . 2 . . . " |
" . H . . . . v . " |
" . . . . . . . . . . . e . " +--+---+
" . t . " | IPv4 |
" . . . . . . , . 3 . " |Server|
" . +----+ v +----+ . " | S2 |
" . | Z += e =+ X7 += . " +------+
" . +-+--+ t +----+ . "
" . | 4 . . . "
" . J . . . . . "
" . . . . . . . "
" 2001:DB8:20::/56 (PI) --------> "
" " " " " " " " " " " " " " "" " " " " " " "
Figure 3: On-Demand Discovery
In this example, tunnel interfaces 'vet1' through 'vet4' as well as
IPv6 PI prefix registrations have been established through VET
enterprise autoconfiguration procedures. When IPv6 end system 'H'
with IPv6 address '2001:DB8:10::1' sends packets to a peer end system
'J' with IPv6 address '2001:DB8:20::1', the packets will be conveyed
through 'V', 'Y1', and finally to 'X2' via default routes. Then,
unless 'X2' has an IPv6 FIB entry matching 'J', it must discover that
'J' can be reached using a more direct route via 'X7' as the next-hop
across the 'E1' commons.
In particular, when 'X2' receives a packet on the 'vet2' interface
with inner destination address 'J', it can perform an on-demand
mapping lookup by consulting the enterprise mapping service, e.g., by
consulting the DNS reverse zone. Alternatively, 'X2' can send the
packet to a default router (e.g., 'R2'), which in turn can forward
the packet to 'X7' and return an ICMPv6 redirect message. When 'X2'
receives the redirect, it can send an RA message to 'X7' to prove
that it is authorized to produce packets with a prefix that matches
source address 'J'. 'X2' can then forward subsequent packets
directly to 'X7' without involving 'R2'.
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In some enterprise scenarios, dynamic routing and on-demand mapping
can be combined as complementary functions. In other scenarios, it
may be preferable to use either dynamic routing only or on-demand
mapping only.
3.3.4. Support for Legacy RLOC-Based Services
Legacy hosts, routers, and networks that were already present in pre-
RANGER deployments and have already numbered their interfaces with
RLOC addresses must see continued support for RLOC-based services for
the long term, even as EID-based services are rolled out in new
deployments. For example, a legacy IPv4-only node behind an IPv4
Network Address Translator (NAT) must still be able to reach legacy
IPv4-only Internet services (e.g., "http://example.com") long after
the RANGER architecture and EID-based services are widely deployed.
Returning to the example diagrams, while virtual enterprise traversal
across 'E1' provides a fully connected routing and addressing
capability for EID-based services, legacy nodes will still require
access to RLOC-based services within connected or disjoint RLOC
spaces for an extended (and possibly indefinite) period. For
example, Figure 4 below depicts the applicable RLOC-based IPv4
service-access scenarios for the RANGER architecture when VET
interfaces are used to link recursively nested enterprises together:
+------+
| IPv6 |
" " " " " " " "" " " " " " " " " " " " " " " " |Server|
" " +--+---+
" . . . . . . . . . . . . . . . " |
" . . . . . . " |
" . +----+ v +--- + v +----+ v +----+ +-----+-------+
" . | V += e =+ Y1 += e =+ X2 += e =+ R2 +==+ Internet |
" . +-+--+ t +----+ t +----+ t +----+ +-----+-------+
" . | 1 . . 2 . . 3 . " |
" . K L . . . . M . " |
" . . . . . . . . . . . . . . " +--+---+
" " | IPv4 |
" " |Server|
" " " " " " " " " " " " " " "" " " " " " " " | S2 |
+------+
Figure 4: Support for Legacy RLOC-Based Services
In a first instance, a legacy RLOC-based IPv4 client 'K' within
enterprise 'E1.1.1' can access RLOC-based IPv4 service 'L' within the
same enterprise as normal and without the need for any encapsulation.
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Instead, 'K' discovers a "mapping" for 'L' through a simple lookup
within the 'E1.1.1' enterprise-local name service, and conveys
packets to 'L' through unencapsulated RLOC-based IPv4 routing and
addressing within the 'E1.1.1' commons. In many instances, this may
indeed be the preferred service-access model, even when EID-based
IPv6 services are widely deployed due to factors such as inability to
replace legacy IPv4 applications, IPv6 header overhead avoidance,
etc.
In a second instance, RLOC-based IPv4 client 'K' can access RLOC-
based IPv4 server 'S2' on the legacy global IPv4 Internet in a number
of ways, based on the way the recursively nested 'E1.*' enterprises
are provisioned:
o if all of the recursively nested 'E1.*' enterprises are configured
within the same IPv4 RLOC space, normal IPv4 forwarding will
convey unencapsulated IPv4 packets from 'K' toward 'R2', which
then acts as an IPv4 Network Address Translator (NAT) and/or an
ordinary IPv4 Enterprise Border Router.
o if the recursively nested 'E1.*' enterprises are configured within
disjoint RLOC spaces, all EBGs 'Y1', 'X2', and 'R2' can be
configured to provide an IPv4 NAT capability (i.e., a recursive
nesting of NATs within NATs). However, this approach places
multiple instances of stateful NAT devices on the path, which can
lead to an overall degree of brittleness and intolerance to
routing changes. Instead, 'R2' can act as a "Carrier-Grade NAT
(CGN)", and 'V' can convey packets from 'K' to the CGN using
IPv4-in-IPv6-in-IPv4 tunneling. The CGN can then decapsulate the
inner, RLOC-based IPv4 packets and translate the IPv4 source
addresses into global IPv4 source addresses before sending the
packets on to 'S2'.
o 'K' could be configured as an EID-based, IPv6-capable node and use
standard IPv6 routing to reach an IPv6/IPv4 translator located at
an EBR for the enterprise in which 'S2' resides. The translator
would then use IPv6-to-IPv4 translation before sending packets
onwards toward 'S2'. These and other alternatives are discussed
in [WING].
In a final instance, RLOC-based IPv4 client 'K' can access an RLOC-
based IPv4 server 'M' in a different enterprise within E1 as long as
both enterprises are configured over the same IPv4 RLOC space. If
the enterprises are configured over disjoint IPv4 RLOC spaces,
however, 'K' would still be able to access 'M' by using EID-based
IPv6 services, by using EID-based IPv4 services if an EID-based IPv4
overlay were deployed, or by using some form of RLOC-based IPv4 NAT
traversal. 'K' could also access server 'M' if both 'V' and 'X2'
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implemented an IPv6/IPv4 protocol translation capability. Finally,
'K' and/or 'M' could implement a bump-in-the-wire or bump-in-the-api
IPv6/IPv4 protocol translation capability.
3.4. Subnetwork Encapsulation and Adaptation Layer (SEAL)
Tunnel endpoints that depend on ICMP feedback from routers within the
enterprise commons may be susceptible to undetected black holes due
to ICMP filtering gateways and/or off-path ICMP spoofing attacks from
a node pretending to be a router. Furthermore, rogue nodes within
enterprises that do not correctly implement ingress filtering can
send spoofed packets of any kind, e.g., for the purpose of mounting
denial-of-service and/or traffic amplification attacks targeting
underprivileged links.
The Subnetwork Encapsulation and Adaptation Layer (SEAL) provisions
each encapsulated packet with a monotonically incrementing, extended
Identification field (i.e., the 32-bit SEAL_ID) that tunnel endpoints
can use as a nonce to detect off-path spoofing. Moreover, tunnel
endpoints that use SEAL can continue to operate correctly even if
some/many ICMPs are lost. Finally, tunnel endpoints that use SEAL
can adapt to subnetworks containing links with diverse MTUs
properties.
3.5. Mobility Management
Enterprise mobility use cases must be considered along several
different vectors:
o nomadic enterprises and end systems may be satisfied to incur
address renumbering events as they move between new enterprise
network attachment points.
o mobile enterprises with PI prefixes may be satisfied by dynamic
updates to the mapping system as long as they do not impart
unacceptable churn.
o mobile enterprises and end systems with PA addresses/prefixes may
require additional supporting mechanisms that can accommodate
address/prefix renumbering.
Nomadic enterprise mobility is already satisfied by currently
deployed technologies. For example, transporting a laptop computer
from a wireless-access hot spot to a home network LAN would allow the
nomadic device to re-establish connectivity at the expense of address
renumbering. Such renumbering may be acceptable, especially for
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devices that do not require session persistence across mobility
events and do not configure servers with addresses published in the
global DNS.
Mobile enterprises with PI prefixes that use VET and SEAL can move
between parent enterprise attachment points as long as they withdraw
the prefixes from the mapping systems of departed enterprises and
inject them into the mapping systems of new enterprises. When moving
between the lower recursive tiers of a common parent enterprise, such
a localized event mobility may result in no changes to the parent
enterprise's mapping system. Hence, the organizational structure of
a carefully arranged enterprise-within-enterprise framework may be
able to dampen mobility-related churn. For enterprises that require
in-the-network confidentiality, IKEv2 Mobility and Multihoming
(MOBIKE) [RFC4555] may also be useful within this context.
Mobile enterprises and end systems that move quickly between
disparate parent enterprise attachment points should not use PI
prefixes if withdrawing and announcing the prefixes would impart
unacceptable mapping/routing churn and packet loss. They should
instead use PA addresses/prefixes that can be coordinated via a
rendezvous service. Mobility management mechanisms such as Mobile
IPv6 [RFC3775] and the Host Identity Protocol (HIP) [RFC4423] can be
used to maintain a stable identifier for fast moving devices even as
they move quickly between visited enterprise attachment points.
As a use case in point, consider an aircraft with a mobile router
moving between ground station points of attachment. If the ground
stations are located within the same enterprise, or within lower-tier
sites of the same parent enterprise, it should suffice for the
aircraft to announce its PI prefixes at its new point of attachment
and withdraw them from the old. This would avoid excessive mapping
system churn, since the prefixes need not be announced/withdrawn
within the parent enterprise, i.e., the churn is isolated to lower
layers of the recursive hierarchy. Note also that such movement
would not entail an aircraft-wide readdressing event.
As a second example, consider a wireless handset moving between
service coverage areas maintained by independent providers with
peering arrangements. Since the coverage range of terrestrial
cellular wireless technologies is limited, mobility events may occur
on a much more aggressive timescale than some other examples. In
this case, the handset may expect to incur a readdressing event for
its access interface at least, and may be obliged to arrange for a
rendezvous service linkage.
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It should specifically be noted that the contingency of mobility
management solutions is not necessarily mutually exclusive and must
be considered in relation to specific use cases. The RANGER
architecture is therefore naturally inclusive in this regard. In
particular, RANGER could benefit from mechanisms that could support
rapid dynamic updates of PI prefix mappings without causing excessive
churn.
3.6. Multihoming
As with mobility management, multihoming use cases must be considered
along multiple vectors. Within an enterprise, EBRs can discover
multiple EBGs and use them in a fault-tolerant and load-balancing
fashion as long as they register their PI prefixes with each such
EBG, as described in Section 3.3.1. These registrations are created
through the transmission of Router Advertisement messages that
percolate up through the recursive enterprise-within-enterprise
hierarchy.
As a first case in point, consider the enterprise network of a major
corporation that obtains services from a number of ISPs. The
corporation should be able to register its PI prefixes with all of
its ISPs, and use any of the ISPs for its Internet access services.
As a second use case, consider an aircraft with a diverse set of
wireless links (e.g., VHF, 802.16, directional, SATCOM, etc.). The
aircraft should be able to select and utilize the most appropriate
link(s) based on the phase of flight and to change seamlessly between
links as necessary. Other examples include a nomadic laptop with
both 802.11 and Ethernet links, a wireless handset with both CDMA
wireless and 802.11, etc.
As with mobility management, the contingency of solutions is not
necessarily mutually exclusive and can combine to suit use cases
within the scope of the RANGER architecture.
3.7. Implications for the Internet
Selection of mapping alternatives may have significant implications
for applications, server selection, route determination, security,
etc. In particular, applications that expect all packets (including
initial ones) to experience similar delays may be adversely affected
by a scheme that imposes non-negligible delays when initial packets
are queued while a look-aside mapping table is consulted. Still
other applications may experience significant startup delays when its
initial packets are dropped during a mapping lookup event. These
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RFC 5720 RANGER February 2010
factors would seem to favor a scheme that is able to forward initial
packets along a path with sub-optimal delay while a mapping lookup is
performed in parallel, e.g., such as when a "default mapper" is used.
Generally speaking, proactive mapping-maintenance mechanisms may have
scaling issues with the amount of updates they generate, while
reactive mechanisms may involve effects to the delay of initial
packets before the cached state is updated. Also to be considered
are attacks against the mapping mechanism, which may result in denial
of service of the mapping cache.
Encapsulation of packets in automatically created tunnels involves a
number of issues as well. There are obvious interactions between
encapsulation overhead and the effective tunnel MTU, which can be
addressed by SEAL and (when necessary) careful operational link
arrangements. Moreover, it is important to minimize the impact to
the global routing table without at the same time impacting the
ability of legacy Internet networks to connect to those employing
RANGER. As long as other nodes in the Internet need to connect to
networks implementing RANGER, EID routes need to appear both in the
mapping system and the global BGP routing tables. This can be
accommodated by keeping the number of prefixes aggregated by RANGER
to the bare minimum through efficient aggregation (e.g., one or a few
[PREF]::/4 IPv6 prefixes instead of millions of [PREF]::/32
prefixes).
4. Related Initiatives
The origins of the RANGER architectural principles can be traced to
the "Catenet model for internetworking" ([CATENET], [IEN48],
[RFC2775]) beginning as early as the mid-1970's. Subsequently,
deliberations of the ROAD group [RFC1380] and related efforts such as
NIMROD [RFC1753] provided a sustained evolution of the concepts.
[RFC1955], "New Scheme for Internet Routing and Addressing (ENCAPS)
for IPNG", captures the high-level architectural aspects of the ROAD
group deliberations.
These foundational works significantly influenced more recent
developments, including the X-Bone initiative [XBONE], which explored
virtual topologies manifested through tunneling. Various tunneling
approaches including IP-in-IP ([RFC2003], [RFC4213]), 6over4
[RFC2529], and ISATAP [RFC5214] have evolved from the mid-1990's
until the present day and are used in common, operational practice.
Tunnel-mode IPsec [RFC4301] is also commonly used for separation of
security domains within enterprises.
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RFC 5720 RANGER February 2010
Currently, initiatives with similar properties to RANGER are under
development within the IRTF Routing Research Group (RRG) and within
IETF working groups such as LISP, SOFTWIRE, V6OPS, and others.
Numerous proposals have been offered within the RRG, including the
Locator-Identifier Split Protocol (LISP) [LISP], Six-One [VOGT], ILNP
[ILNP], Internet vastly improved plumbing (Ivip) [WHITTLE], A
Practical Transit-Mapping Service (APT) [JEN], and Virtual
Aggregation [VA]. Still other similar initiatives almost certainly
exist.
While RANGER shares many properties with these earlier works, it
uniquely provides a top-to-bottom articulation of how the various
pieces fit together within a recursively nested "enterprise-within-
enterprise" (or "network-of-networks") framework. In this way, it
bears striking resemblance to the network-of-networks model
envisioned by CATENET. RANGER further provides a detailed
consideration of challenging issues such as autoconfiguration,
provider-independent addressing, border router discovery, tunnel MTU,
multihoming, etc. that many other approaches have either overlooked
or left for future work. A detailed analysis of RANGER applicability
in various use case scenarios is provided in "RANGER Scenarios
(RANGERS)" [RUSSERT].
5. Security Considerations
Communications between endpoints within different sites inside an
enterprise are carried across a commons that joins organizational
entities with a mutual spirit of cooperation, but between which there
may be competing business/sociological/political interests. As a
result, mechanisms that rely on feedback from routers on the path may
become brittle or susceptible to spoofing attacks. This is due to
the fact that IP packets can be lost due to congestion or packet-
filtering gateways and that the source addresses of IP packets can be
forged. Moreover, IP packets in general can be generated by
anonymous attackers, e.g., from a rogue node within a third-party
enterprise that has malicious intent toward a victim.
Path MTU Discovery is an example of a mechanism that relies on ICMP
feedback from routers on the path and, as such, is susceptible to
these issues. For IPv4, a common workaround is to disable Path MTU
Discovery and let fragmentation occur in the network if necessary.
For IPv6, lack of fragmentation support in the network precludes this
option such that the mitigation typically recommended is to discard
ICMP messages that contain insufficient information and/or to operate
with the minimum IPv6 path MTU. This example extends also to other
mechanisms that either rely on or are enhanced by feedback from
network devices; however, attack vectors based on non-ICMP messages
are also subject for concern.
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RFC 5720 RANGER February 2010
The RANGER architecture supports effective mitigations for attacks
such as distributed denial-of-service, traffic amplification, etc.
In particular, when VET and SEAL are used, EBGs can use the 32-bit
identification encoded in the SEAL header as well as ingress
filtering to determine if a message has come from a topologically
correct enterprise located across the commons. This allows
enterprises to employ effective mitigations at their borders without
the requirement for mutual cooperation from other enterprises. When
source address spoofing by on-path attackers located within the
commons is also subject for concern, additional securing mechanisms
such as tunnel-mode IPsec between enterprise EBGs can also be used.
EBRs can obtain PI prefixes through arrangements with a prefix
delegation authority. Thereafter, the EBR can announce and/or
withdraw the prefixes within an enterprise by sending IPv6 Router
Advertisements (RAs). In environments where additional
authenticating mechanisms are necessary, the EBR can sign its RAs
using SEcure Neighbor Discovery (SEND) [RFC3971].
While the RANGER architecture does not in itself address security
considerations, it proposes an architectural framework for functional
specifications that do. Security concerns with tunneling, along with
recommendations that are compatible with the RANGER architecture, are
found in [HOAGLAND].
6. Acknowledgements
This work was inspired through the encouragement of the Boeing DC&NT
network technology team and through the communications of the IESG.
Many individuals have contributed to the architectural principles
that form the basis for RANGER over the course of many years. The
following individuals have given specific feedback on the RANGER
document itself: Jari Arkko, Brian Carpenter, Eric Fleischman, Joel
Halpern, Thomas Henderson, Steven Russert, Dallas Thomas, Robin
Whittle.
7. References
7.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
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RFC 5720 RANGER February 2010
7.2. Informative References
[CATENET] Pouzin, L., "A Proposal for Interconnecting Packet
Switching Networks", Proceedings of EUROCOMP, Bronel
University, p. 1023-1036, May 1974.
[COEXIST] Arkko, J. and M. Townsley, "IPv4 Run-Out and IPv4-IPv6 Co-
Existence Scenarios", Work in Progress, July 2009.
[BAUER] Bauer, C. and S. Ayaz, "ATN Topology Considerations for
Aeronautical NEMO RO", Work in Progress, September 2009.
[LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol (LISP)", Work in Progress,
September 2009.
[HOAGLAND] Hoagland, J., Krishnan, S., and D. Thaler, "Security
Concerns With IP Tunneling", Work in Progress, October
2008.
[JEN] Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
L. Zhang, "APT: A Practical Transit Mapping Service", Work
in Progress, November 2007.
[RUSSERT] Russert, S., Fleischman, E., and F. Templin, "RANGER
Scenarios", Work in Progress, September 2009.
[SEAL] Templin, F., Ed., "The Subnetwork Encapsulation and
Adaptation Layer (SEAL)", RFC 5320, February 2010.
[VET] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, February 2010.
[WING] Wing, D., Ward, D., and A. Durand, "A Comparison of
Proposals to Replace NAT-PT", Work in Progress, September
2008.
[IEN48] Cerf, V., "The Catenet Model for Internetworking", July
1978.
[ILNP] Atkinson, R., "ILNP Concept of Operations", Work in
Progress, December 2008.
[RFC1380] Gross, P. and P. Almquist, "IESG Deliberations on Routing
and Addressing", RFC 1380, November 1992.
Templin Informational [Page 24]
RFC 5720 RANGER February 2010
[RFC1753] Chiappa, N., "IPng Technical Requirements Of the Nimrod
Routing and Addressing Architecture", RFC 1753, December
1994.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC1955] Hinden, R., "New Scheme for Internet Routing and
Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, February
2000.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, June 2006.
[RFC4852] Bound, J., Pouffary, Y., Klynsma, S., Chown, T., and D.
Green, "IPv6 Enterprise Network Analysis - IP Layer 3
Focus", RFC 4852, April 2007.
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RFC 5720 RANGER February 2010
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[VA] Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
L. Zhang, "FIB Suppression with Virtual Aggregation", Work
in Progress, October 2009.
[VOGT] Vogt, C., "Six/One: A Solution for Routing and Addressing
in IPv6", Work in Progress, October 2009.
[WHITTLE] Whittle, R., "Ivip (Internet Vastly Improved Plumbing)
Architecture", Work in Progress, August 2008.
[XBONE] Touch, J., "The X-Bone", March 1997,
http://www.isi.edu/touch/pubs/ngi97/x-bone-ngi97.pdf
Author's Address
Fred L. Templin
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
EMail: fltemplin@acm.org
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